Loop or ring data communication networks are well known in the art. It is also well known to provide a double loop for such networks to ensure the availability of a communication path if failure in a node or in a portion of a path should occur. Such systems usually require constant checking of the system to detect for the occurrence of a fault and means for reconfiguring the two loops to form a single loop including a bypass around the fault, should one occur. Thus, under no fault operation, a double data path is provided. But when a fault occurs a local bypass about the fault is provided at the expense of throughput.
U.S. Pat. No. 4,553,233 issued Nov. 12, 1985, and assigned to International Standard Electric Corporation discloses one such system which requires no central processor but a relatively sophisticated node configuration. U.S. Pat. No. 4,542,496 issued Sept. 17, 1985, and assigned to Fujitzu Limited discloses a system of the type which does employ a central processor. In this latter system, the central processor is operative to check for the occurrence of a fault and to switch transmission to the alternative loop if such is available. If a fault occurs in both loops at once, the central processor connects the two loops at the nodes to either side of the fault in order to provide a transmission path.
Prior art systems of this type require fairly expensive node configurations, critical timing, and expensive wiring configurations which limit the use of such systems.